The present invention relates to a work machine comprising a front section with a front frame, a first set of ground engaging members and a power source for propelling the work machine, a rear section with a rear frame, a second set of ground engaging members and a load-carrying container.
The invention will below be described for an articulated hauler. This should however be regarded as a non-limiting example. The invention may be realized in other types of work machines, such as dump trucks or other construction equipment having a tractor unit and a trailer unit which are pivotally connected to each other. The expression “work machine” is also intended to comprise heavy vehicles to be used on regular roads, such as trucks having a front section (tractor or semitrailer tractor unit) and a rear section (trailer or semi-trailer unit) pulled by the front section.
Further terms frequently used for work machines are “earth-moving machinery”, “off-road work machines”, “construction equipment” and “forest machines”. The term “ground engaging members” may comprise wheels, caterpillar tracks etc.
In connection with transportation of heavy loads, e.g. in contracting work, a work machine of the type of an articulated hauler is frequently used. Such vehicles may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines, forestry and similar environments. Thus, an articulated hauler is frequently used in rough terrain with various slippery ground.
The front frame carries a power source in the form of an internal combustion engine and a load-carrying container is arranged on the rear frame of an articulated hauler. An articulated hauler is further defined by a first pivot joint arranged to allow the front frame and the rear frame to pivot in relation to each other around an imaginary longitudinal axis, that is an axis that runs in the longitudinal direction of the vehicle. Travelling on uneven ground is substantially improved by virtue of such a joint.
The articulated hauler further has a second, vertical pivot joint between the front frame and the rear frame and a pair of hydraulic cylinders for steering the work machine via pivoting the front frame relative to the rear frame about the vertical pivot axis. It is emphasized that a frame-steered work machine is adapted for an optimized off road performance with regard to any vehicle with Ackerman steering (front wheel steering). More specifically, the articulated steering creates conditions for using much larger (both with regard to diameter and width) front wheels than with so-called Ackermann steering. Further, articulated steering creates conditions for 100% lock in the front axle differential (which is not possible with Ackermann steering), which is essential when operating on slippery ground.
Further, an articulated hauler normally has six wheels.
The front section comprises a front wheel axle and the rear section comprises a pair of bogie axles. A powertrain is adapted to drive the three wheel axles. Thus, the articulated hauler may be operated with all (6) wheel drive.
Each axle is provided with a differential gear and a (transverse) differential lock. Further, one longitudinal differential lock is provided on the transmission shaft between the front axle and the bogie axles and a further longitudinal differential lock is provided on the transmission shaft between the bogie axles. The differential locks are preferably engaged when there is a risk of the wheels slipping. According to an alternative design, any of the differential locks may be replaced by a device allowing limited slip.
It is desirable to achieve a work machine, which creates conditions for a more flexible operation.
In a work machine according to an aspect of the present invention, the rear section comprises an electric drive system adapted for driving at least one ground engaging member of said second set, that the rear section is detachably connected to the front section, that the power source of the front section is adapted to power the electric drive system in the rear section in an attached state of the front and rear sections, and that said electric drive system is adapted for driving said at least one ground engaging member of said second set for self-propelling of the rear section in a detached state.
Thus, the invention is particularly directed, according to an aspect thereof, to a hybrid electric work machine.
Thus, the rear section can be maneuvered after disconnection. In other words, the invention creates conditions for detaching the rear section and self-propelling the rear section short distances.
Preferably, a control system is adapted for remote control of the rear section in order to maneuver it in the detached state. The control system is preferably adapted for communication between a remote unit and the detached rear section via radio waves.
According to an example, the electric drive system comprises at least one electric motor. The electric motor creates conditions for an infinitely variable torque distribution between the wheels which is advantageous when operating in severe terrain conditions.
According to a preferred embodiment, the power source comprises an electric machine for providing electric power. Preferably, the power source comprises means for generating mechanical power and the electric machine is operatively connected to the mechanical power generating means for converting the mechanical power to electric power. Especially, the means for generating mechanical power is constituted by an internal combustion engine and the electric machine forms a generator. Alternatively, the electric machine may be adapted to generate electric power directly (for example a fuel cell).
Further, torque may be infinitely variably supplied to the rear wheels in order to support the front wheel drive in certain (slippery) conditions.
Further preferred embodiment and advantages thereof emerge from the description below, the figures and the claims.